This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our current Ku-band ESR microimaging system includes a large (15 inch pole face) resistive magnet that provides good working space for ESR microimaging (ESRM) development purposes but is powered by an older Varian V-2500 linear regulated power source to which we have attached a patchwork of several discrete feedback systems for the purpose of accurate field regulation. Currently the feedback systems include a Hall-input Field Dial console, a Lakeshore model 475 Hall field controller and a modified Varian V-4542 field/frequency lock (FFL) system consisting of EPR probe and signal processing electronics. Although this system has performed in a generally satisfactory manner to date, its reliability is marginal, particularly when operating in (Hall-stabilized) field regulation mode for setup purposes, and its use, from an operational viewpoint, is unnecessarily complicated. During the course of upgrading to the new 15KW Gensys magnet power supply (Subproject 0218), we propose replacing the existing regulation system with a newly-designed hybrid system incorporating the present Lakeshore 475 Hall field controller and Varian V-4542 field/frequency lock probe, adding the necessary mode control electronics and communication channel to the Gensys power source. This highly integrated regulation system will also include the programmable precision reference required for offsetting the relatively low resolution (16bit) Lakeshore controller output to achieve ca 20b/10 mG resolution to 1.0T. An option for input dithering can also be included as may be required. Provision is included in current design specification for full remote control of programmable field regulation parameters and functional modes so that the system can operate compatibly with the ESRM LabView VI (virtual instrument) software. We plan to employ essentially the same design in the construction of a second hybrid regulation system to provide Hall/FFL magnetic field control for our proposed 35 GHz ESR microscope (Subproject 0138).